La Lanthanum

Quick answerLanthanum (La) is a lanthanide with atomic number 57 and an atomic mass of 138.91 (2023), in period 6. It was discovered by Carl Gustaf Mosander in 1839. It is used for camera lenses and hybrid car batteries. Its electron configuration is [Xe] 5d1 6s2.

Lanthanum is the first lanthanide, and its compounds sharpen camera lenses, store hydrogen, and light hybrid car batteries.

Key facts

Symbol	La
Atomic number	57
Atomic mass	138.91 (IUPAC standard atomic weight, 2023)
Category	lanthanide
Group	— (f-block element, no group number)
Period	6
Block	f-block
Electron configuration	[Xe] 5d1 6s2
Discovered	Carl Gustaf Mosander, 1839
Uses	camera lenses, hybrid car batteries, hydrogen storage, catalysts, carbon arc lamps

Quick quiz

Three questions from the facts on this page. No sign-up, no score is saved.

1. What is the chemical symbol of Lanthanum?

La Nd Pr Ce

2. What is the atomic number of Lanthanum?

58 59 56 57

3. Which category does Lanthanum belong to?

noble gas alkali metal halogen lanthanide

Check my answers

Keep exploring

• Periodic table — all 118 elements
• Cerium (Ce) — another lanthanide, atomic number 58
• Praseodymium (Pr) — another lanthanide, atomic number 59
• Neodymium (Nd) — another lanthanide, atomic number 60
• Promethium (Pm) — another lanthanide, atomic number 61
• Samarium (Sm) — another lanthanide, atomic number 62
• Europium (Eu) — another lanthanide, atomic number 63
• Gadolinium (Gd) — another lanthanide, atomic number 64
• Terbium (Tb) — another lanthanide, atomic number 65
• Dysprosium (Dy) — another lanthanide, atomic number 66
• Holmium (Ho) — another lanthanide, atomic number 67
• All lanthanide elements — on the periodic table

Sources & last updated

• CIAAW — Standard Atomic Weights
• PubChem Periodic Table
• Wikipedia — Timeline of chemical element discoveries
• Wikipedia — Lanthanum

Last updated: 2026-11-12. Figures are shown with their year; where sources disagree, the value is left out rather than estimated.